While other group 8 elements have two electrons in the outermost shell, in ruthenium the outermost shell has only one electron (the final electron is in a lower shell). This anomaly, which has no effect on chemical properties, is also observed in all other elements (excepttechnetium) in the range ofZ = 41-45.[15]
Ruthenium has four crystal modifications and does not tarnish at ambient conditions; it oxidizes upon heating to 800 °C (1,070 K). Ruthenium dissolves in fused alkalis to give ruthenates (RuO2− 4). It is not attacked by acids (evenaqua regia) but is attacked by sodium hypochlorite at room temperature, andhalogens at high temperatures.[14] Ruthenium is most readily attacked by oxidizing agents.[16] Small amounts of ruthenium can increase the hardness ofplatinum andpalladium. Thecorrosion resistance oftitanium is increased markedly by the addition of a small amount of ruthenium.[14] The metal can be plated byelectroplating and by thermal decomposition. A ruthenium–molybdenum alloy is known to besuperconductive at temperatures below 10.6 K.[14] Ruthenium is the only 4d transition metal that can assume the oxidation state +8, and even then it is less stable there than the heavier congener osmium: this is the first group from the left of the table where the second and third-row transition metals display notable differences in chemical behavior. Like iron but unlike osmium, ruthenium can form aqueous cations in its lower oxidation +2 and +3 states.[17]
Ruthenium is the first in a downward trend in the melting and boiling points and atomization enthalpy in the 4d transition metals after the maximum seen atmolybdenum, because the 4d subshell is more than half full and the electrons are contributing less to metallic bonding. (Technetium, the previous element, has an exceptionally low value that is off the trend due to its half-filled [Kr]4d55s2 configuration, though it is not as far off the trend in the 4d series asmanganese in the 3d transition series.)[18] Unlike the lighter congener iron, ruthenium is usuallyparamagnetic at room temperature, as iron also is above itsCurie point.[19] However, the metastable tetragonal phase of ruthenium, created as a thin film on single crystal Mo, is ferromagnetic at room temperature.[20]
The reduction potentials in acidic aqueous solution for some common ruthenium species are shown below:[21]
Naturally occurring ruthenium is composed of seven stableisotopes: 96, 98-102, 104.[22] Additionally, 34 syntheticradioactive isotopes have been discovered. Of theseradioisotopes, the most stable are106Ru with ahalf-life of 371.8 days,103Ru with a half-life of 39.245 days and97Ru with a half-life of 2.837 days.[23]
Fifteen other radioisotopes have been characterized ranging from85Ru to125Ru. Most of these have half-lives that are less than five minutes; the exceptions are94Ru (51.8 minutes),95Ru (1.607 hours), and105Ru (4.44 hours).[23]
Ruthenium is found in about 100 parts per trillion in the Earth's crust, making it the78th most abundant element.[26] It is generally found in ores with the other platinum group metals in theUral Mountains and in North and South America. Small but commercially important quantities are also found inpentlandite extracted fromSudbury,Ontario, Canada, and inpyroxenite deposits inSouth Africa. The native form of ruthenium is a very rare mineral (Ir replaces part of Ru in its structure).[27][28]
Roughly 30 tonnes of ruthenium are mined each year,[29] and world reserves are estimated at 5,000 tonnes.[30] The composition of the minedplatinum group metal (PGM) mixtures varies widely, depending on the geochemical formation. For example, the PGMs mined in South Africa contain on average 11% ruthenium while the PGMs mined in the former USSR contain only 2% (1992).[31][32] Ruthenium, osmium, and iridium are considered the minor platinum group metals.[19]
Ruthenium, like the other platinum group metals, is obtained commercially as a by-product from processing ofnickel,copper, and platinum metal ore. Duringelectrorefining of copper and nickel, noble metals such as silver, gold, and the platinum group metals precipitate asanode mud, thefeedstock for the extraction.[27][28] The metals are converted to ionized solutes by any of several methods, depending on the composition of the feedstock. One representative method is fusion withsodium peroxide followed by dissolution inaqua regia, and solution in a mixture ofchlorine withhydrochloric acid.[33][34]Osmium (Os), ruthenium (Ru),rhodium (Rh), andiridium (Ir) are insoluble in aqua regia and readily precipitate, leaving the other metals in solution. Rhodium is separated from the residue by treatment with molten sodium bisulfate. The insoluble residue, containing Ru, Os, and Ir is treated with sodium oxide, in which Ir is insoluble, producing dissolved Ru and Os salts. After oxidation to the volatile oxides,RuO 4 is separated fromOsO 4 by precipitation of (NH4)3RuCl6 with ammonium chloride or by distillation or extraction with organic solvents of the volatile osmium tetroxide.[35]Hydrogen is used to reduceammonium ruthenium chloride, yielding a powder.[14][36] The product is reduced using hydrogen, yielding the metal as a powder orsponge metal that can be treated withpowder metallurgy techniques orargon-arc welding.[14][37]
Ruthenium can also be produced by deliberatenuclear transmutation from99 Tc. Given its relatively long half-life, highfission product yield and high chemical mobility in the environment,99 Tc is among the most often proposed non-actinides for commercial-scale nuclear transmutation.99 Tc has a relatively largeneutron cross section, and because technetium has no stable isotopes, there would not be a problem ofneutron activation of stable isotopes. Significant amounts of99 Tc are produced in nuclear fission. They are also produced as a byproduct of the use of99m Tc innuclear medicine, because this isomer decays to99 Tc. Exposing the99 Tc target to strong enoughneutron radiation will eventually yield appreciable quantities of ruthenium, which can be chemically separated while consuming99 Tc.[40][41]
Theoxidation states of ruthenium range from −2 to +8. The properties of ruthenium and osmiumcompounds are often similar. The +2, +3, and +4 states are the most common. The most prevalent precursor isruthenium trichloride, a red solid that is poorly defined chemically but versatile synthetically.[36]
Ruthenium can beoxidized toruthenium(IV) oxide (RuO2, oxidation state +4), which can, in turn, be oxidized bysodium metaperiodate to the volatile yellow tetrahedralruthenium tetroxide, RuO4, an aggressive, strong oxidizing agent with structure and properties analogous toosmium tetroxide. RuO4 is mostly used as an intermediate in the purification of ruthenium from ores and radiowastes.[42]
Dipotassium ruthenate (K2RuO4, +6) and potassium perruthenate (KRuO4, +7) are also known.[43] Unlike osmium tetroxide, ruthenium tetroxide is less stable, is strong enough as an oxidizing agent to oxidize dilutehydrochloric acid and organic solvents likeethanol at room temperature, and is easily reduced to ruthenate (RuO2− 4) in aqueous alkaline solutions; it decomposes to form the dioxide above 100 °C. Unlike iron but like osmium, ruthenium does not form oxides in its lower +2 and +3 oxidation states.[44] Ruthenium forms dichalcogenides, which are diamagnetic semiconductors crystallizing in thepyrite structure.[44] Ruthenium sulfide (RuS2) occurs naturally as the minerallaurite.[45]
Like iron, ruthenium does not readily form oxoanions and prefers to achieve high coordination numbers with hydroxide ions instead. Ruthenium tetroxide is reduced by cold dilutepotassium hydroxide to form black potassium perruthenate, KRuO4, with ruthenium in the +7 oxidation state. Potassium perruthenate can also be produced by oxidizing potassium ruthenate, K2RuO4, with chlorine gas. The perruthenate ion is unstable and is reduced by water to form the orange ruthenate. Potassium ruthenate may be synthesized by reacting ruthenium metal with molten potassium hydroxide andpotassium nitrate.[46]
Some mixed oxides are also known, such as MIIRuIVO3, Na3RuVO4, Na 2RuV 2O 7, and MII 2LnIII RuV O 6.[46]
The highest known ruthenium halide is thehexafluoride, a dark brown solid that melts at 54 °C. It hydrolyzes violently upon contact with water and easily disproportionates to form a mixture of lower ruthenium fluorides, releasing fluorine gas.Ruthenium pentafluoride is a tetrameric dark green solid that is also readily hydrolyzed, melting at 86.5 °C. The yellowruthenium tetrafluoride is probably also polymeric and can be formed by reducing the pentafluoride withiodine. Among the binary compounds of ruthenium, these high oxidation states are known only in the oxides and fluorides.[47]
Ruthenium trichloride is a well-known compound, existing in a black α-form and a dark brown β-form: the trihydrate is red.[48] Of the known trihalides, trifluoride is dark brown and decomposes above 650 °C, tribromide is dark-brown and decomposes above 400 °C, and triiodide is black.[47] Of the dihalides, difluoride is not known, dichloride is brown, dibromide is black, and diiodide is blue.[47] The only known oxyhalide is the pale green ruthenium(VI) oxyfluoride, RuOF4.[48]
Though naturally occurring platinum alloys containing all sixplatinum-group metals were used for a long time bypre-Columbian Americans and known as a material to European chemists from the mid-16th century, not until the mid-18th century was platinum identified as a pure element. That natural platinum contained palladium, rhodium, osmium and iridium was discovered in the first decade of the 19th century.[52] Platinum inalluvial sands of Russian rivers gave access to raw material for use in plates and medals and for the minting ofrublecoins, starting in 1828.[53]
It is possible that thePolish chemistJędrzej Śniadecki isolated element 44 (which he called "vestium" after the asteroidVesta discovered shortly before) from South American platinum ores in 1807. He published an announcement of his discovery in 1808.[54] His work was never confirmed, however, and he later withdrew his claim of discovery.[30]
Jöns Berzelius andGottfried Osann nearly discovered ruthenium in 1827.[55] They examined residues that were left after dissolving crude platinum from theUral Mountains inaqua regia. Berzelius did not find any unusual metals, but Osann thought he found three new metals, which he called pluranium, ruthenium, and polinium.[14] This discrepancy led to a long-standing controversy between Berzelius and Osann about the composition of the residues.[56][57] As Osann was not able to repeat his isolation of ruthenium, he eventually relinquished his claims.[56][58] The name "ruthenium" was chosen by Osann because the analyzed samples stemmed from the Ural Mountains in Russia.[59]
In 1844,Karl Ernst Claus, a Russian scientist ofBaltic German descent, showed that the compounds prepared by Gottfried Osann contained small amounts of ruthenium, which Claus haddiscovered the same year.[14][52] Claus isolated ruthenium from the platinum residues of rouble production while he was working inKazan University,Kazan,[56] the same way its heavier congener osmium had been discovered four decades earlier.[26] Claus showed that ruthenium oxide contained a new metal and obtained 6 grams of ruthenium from the part of crude platinum that is insoluble inaqua regia.[56] Choosing the name for the new element, Claus stated: "I named the new body, in honour of my Motherland, ruthenium. I had every right to call it by this name because Mr. Osann relinquished his ruthenium and the word does not yet exist in chemistry."[56][57] The name itself derives from the Latin wordRuthenia.[8][9]In doing so, Claus started a trend that continues to this day – naming an element after a country.[60]
Approximately 30.9 tonnes of ruthenium were consumed in 2016, 13.8 of them in electrical applications, 7.7 in catalysis, and 4.6 in electrochemistry.[29]
Because it hardens platinum and palladium alloys, ruthenium is used inelectrical contacts, where a thin film is sufficient to achieve the desired durability. With its similar properties to and lower cost than rhodium,[37] electric contacts are a major use of ruthenium.[27][61] The ruthenium plate is applied to the electrical contact and electrode base metal by electroplating[62] orsputtering.[63]
Ruthenium dioxide withlead andbismuth ruthenates are used in thick-film chip resistors.[64][65][66] These two electronic applications account for 50% of the ruthenium consumption.[30]
Ruthenium is occasionally alloyed with metals outside the platinum group, where small quantities improve some properties. The added corrosion resistance intitanium alloys led to the development of a special alloy with 0.1% ruthenium.[67] Ruthenium is also used in some advanced high-temperature single-crystalsuperalloys, with applications that include the turbines injet engines. Several nickel based superalloy compositions are described, such as EPM-102 (with 3% Ru), TMS-162 (with 6% Ru), TMS-138,[68] and TMS-174,[69][70] the latter two containing 6%rhenium.[71]Fountain pen nibs are frequently tipped with ruthenium alloy. From 1944 onward, theParker 51 fountain pen was fitted with the "RU" nib, a 14K gold nib tipped with 96.2% ruthenium and 3.8%iridium.[72]
Ruthenium is a component ofmixed-metal oxide (MMO) anodes used for cathodic protection of underground and submerged structures, and for electrolytic cells for such processes asgenerating chlorine from salt water.[73] Thefluorescence of some ruthenium complexes is quenched by oxygen, finding use inoptode sensors for oxygen.[74]Ruthenium red, [(NH3)5Ru-O-Ru(NH3)4-O-Ru(NH3)5]6+, is abiological stain used to stainpolyanionic molecules such aspectin andnucleic acids forlight microscopy andelectron microscopy.[75] The beta-decaying isotope 106 of ruthenium is used in radiotherapy of eye tumors, mainlymelanomas of theuvea.[76] Ruthenium-centered complexes are being researched for possible anticancer properties.[77] The "piano-stool" Ru(II) compounds show promise to replace current platinum-based anti-tumor drugs.[78]
Ruthenium tetroxide exposes latent fingerprints by reacting on contact with fatty oils or fats with sebaceous contaminants and producing brown/black ruthenium dioxide pigment.[79]
Many ruthenium-containing compounds exhibit useful catalytic properties. Solutions containingruthenium trichloride are highly active forolefin metathesis. Such catalysts are used commercially for the production of polynorbornene for example.[84] Well defined rutheniumcarbene andalkylidene complexes show similar reactivity but are only used on small-scale.[85] TheGrubbs' catalysts, for example, have been employed in the preparation of drugs and advanced materials.[86]
Little is known about the health effects of ruthenium[93] and it is relatively rare for people to encounter ruthenium compounds.[94] Metallic ruthenium isinert (is notchemically reactive).[93] Some compounds such asruthenium tetroxide (RuO4) are highly toxic and volatile.[94]
^abcdArblaster, John W. (2018).Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International.ISBN978-1-62708-155-9.
^Ru(–1) occurs in [Ru2(CO)8]2–; seeXuenian Chen; Hima Kumar Lingam; Edward A. Meyers; Sheldon G. Shore (2012). "Structures of DMF solvated potassium and sodium salts of [Fe(CO)4]2– and [M2(CO)8]2– (M = Fe, Ru)".Journal of Organometallic Chemistry.721–722:137–143.doi:10.1016/j.jorganchem.2012.07.040.
^Ru(0) is present in the carbonyl-phosphine complex Ru(CO)2(PPh3)3, seeStephane Sentets; Maria del Carmen Rodriguez Martinez; Laure Vendier; Bruno Donnadieu; Vincent Huc; Noël Lugan; Guy Lavigne (2005). "Instant "Base-Promoted" Generation of Roper's-type Ru(0) Complexes Ru(CO)2(PR3)3 from a Simple Carbonylchlororuthenium(II) Precursor".J. Am. Chem. Soc.127 (42):14554–14555.doi:10.1021/ja055066e.PMID16231891.
^abcLoferski, Patricia J.; Ghalayini, Zachary T. and Singerling, Sheryl A. (2018)Platinum-group metals.2016 Minerals Yearbook. USGS. p. 57.3.
^abcEmsley, J. (2003)."Ruthenium".Nature's Building Blocks: An A-Z guide to the elements. Oxford, UK: Oxford University Press. pp. 368–370.ISBN978-0-19-850340-8 – via archive.org.
^Renner, Hermann; Schlamp, Günther; Kleinwächter, Ingo; Drost, Ernst; Lüschow, Hans Martin; Tews, Peter; et al. (2001). "Platinum group metals and compounds".Ullmann's Encyclopedia of Industrial Chemistry.doi:10.1002/14356007.a21_075.ISBN978-3-527-30673-2.
^Swain, Pravati; Mallika, C.; Srinivasan, R.; Mudali, U. Kamachi; Natarajan, R. (November 2013). "Separation and recovery of ruthenium: A review".Journal of Radioanalytical and Nuclear Chemistry.298 (2):781–796.Bibcode:2013JRNC..298..781S.doi:10.1007/s10967-013-2536-5.S2CID95804621.
^abClaus, Karl (1845). "О способе добывания чистой платины из руд" [On the method of extracting pure platinum from ores].Горный Журнал (Mining Journal) (in Russian).7 (3):157–163.
^Rao, C.; Trivedi, D. (2005). "Chemical and electrochemical depositions of platinum group metals and their applications".Coordination Chemistry Reviews.249 (5–6): 613.Bibcode:2005CooCR.249..613R.doi:10.1016/j.ccr.2004.08.015.
^Busana, M. G.; Prudenziati, M.; Hormadaly, J. (2006). "Microstructure development and electrical properties of RuO2-based lead-free thick film resistors".Journal of Materials Science: Materials in Electronics.17 (11): 951.doi:10.1007/s10854-006-0036-x.hdl:11380/303403.S2CID135485712.
^Bondarenko, Yu. A.; Kablov, E. N.; Surova, V. A.; Echin, A. B. (2006). "Effect of high-gradient directed crystallization on the structure and properties of rhenium-bearing single-crystal alloy".Metal Science and Heat Treatment.48 (7–8): 360.Bibcode:2006MSHT...48..360B.doi:10.1007/s11041-006-0099-6.S2CID136907279.
^Kwon, Oh-Kyum; Kim, Jae-Hoon; Park, Hyoung-Sang; Kang, Sang-Won (2004). "Atomic Layer Deposition of Ruthenium Thin Films for Copper Glue Layer".Journal of the Electrochemical Society.151 (2): G109.Bibcode:2004JElS..151G.109K.doi:10.1149/1.1640633.
^Vasilyev, V. Yu. (2010). "Low-temperature pulsed CVD of ruthenium thin films for micro- and nanoelectronic applications, Part 1: Equipment and methodology".Russian Microelectronics.39:26–33.doi:10.1134/S106373971001004X.S2CID122854468.
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